The concept of hysteresis is somewhat known, in that a system does not immediately respond to a stimulus, but has some delay associated with that response. This effect is oftentimes desired in many applications. For example, the thermostat of a heater or air conditioner must have a certain amount of hysteresis, otherwise the heater or air conditioner would cycle on and off at a rapid rate once the temperature reached the thermostat setting. With hysteresis, the thermostat or controller which controls operation of the air conditioning system will not turn on the moment the ambient temperature reaches the thermostat setting or slightly exceeds that setting, but instead is delayed. In a general sense, such controllers are oftentimes referred to as “hysteretic controllers.” Hysteretic controllers can be used in numerous applications, well beyond the example of an air conditioner or heater. Most hysteretic controllers follow the concept of the hysteresis loop, and take advantage of the affects of hysteresis by turning off and on a delayed time after reaching upper and lower threshold limits, respectively. Thus, most hysteretic controllers implement some form of upper and lower threshold limits to engage and disengage the control function.
While hysteretic controllers are prevalent in many systems, the timing in which they are engaged or active, or when disengaged or inactive, oftentimes depends on the components of the system, beyond just the environment in which they operate. For example, the components of the hysteretic controller can change over temperature or time, or simply change due to design flaws which are inherent in their operation. If so, the phase relationship of when the controller becomes active or inactive can rapidly change, creating circuit operation problems. This deleterious effect becomes profound when a controller is desired to activate a load or deactivate a load at a specific time, yet does so at unacceptable times well beyond the normal hysteretic lag.